Nanofiber surface based capacitors

ABSTRACT

This invention provides novel capacitors comprising nanofiber enhanced surface area substrates and structures comprising such capacitors, as well as methods and uses for such capacitors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of, and priority to, U.S. ProvisionalApplication No. 60/554,549 filed Mar. 18, 2004. This prior applicationis hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates primarily to the field of nanotechnology. Morespecifically, the invention pertains to capacitors comprising nanofibersand nanofiber enhanced surface areas, as well as to the use of suchcapacitors in various applications and devices.

BACKGROUND OF THE INVENTION

Various configurations of nanostructures (e.g., nanofibers, nanowires,nanocrystals, etc.) have attracted widespread interest for their novelproperties in electrical, chemical, optical and other similarapplications. Nanostructures have a broad possibility of uses, such assemiconductors for nanoscale electronics, optoelectronic applications(e.g., in lasers, LEDs, etc.) photovoltaics, sensors, etc.

Correspondingly, capacitors are pervasive electronic elements. Often, itis quite desirous to place capacitors of particular capacitance,durability, and/or construction within extremely small spaces.

In almost all instances, however, the efficiency or use of such devicesis limited, at least in part, by the area of the surface which is incontact with, or comprises, the electrode plates of the capacitor. Thislimitation is true in several aspects. First, space limitations (or“footprint” limitations) are of concern. For example, for definedmaterials, a certain capacitance can exist per unit area of a surface(i.e., within a certain footprint area). Thus, the capacitance islimited by, inter alia, the footprint of the surfaces which comprise thecapacitor. One answer to such problem is to increase the size of thefootprint involved. However, besides being inelegant, such response isoften problematic due to cost restraints and size limitations imposed onthe footprint itself (e.g., the capacitor might need to be placed in alimited space in a device, etc.)

In a number of conventional or current applications, the surface area ofa capacitor's electrode surface is increased by providing the materialmaking up the surface with a number of holes or pores (e.g., by etchinga metal plate, etc.). By providing such matrix as a porous solid, ratherthan just a solid surface, one increases the amount of available surfacearea without increasing the amount of space that the material occupies(i.e., the footprint size). While such porous matrices do increase thesurface area of the electrode surface, a number of issues arise to limitthe effectiveness of such measures. A final, but not trivial, problemconcerns cost. Larger devices/surfaces/structures that are needed, e.g.,to allow the proper capacitance, can be quite expensive.

Thus, a welcome addition to the art would be capacitors (and devices,etc. comprising capacitors) which have enhanced surface areas whichwould have the benefits of, e.g., increased capacitance per unit areafootprint. The current invention provides these and other benefits whichwill be apparent upon examination of the following.

SUMMARY OF THE INVENTION

In some aspects the current invention comprises an electric capacitorwhich has at least one electrode surface that comprises a plurality ofnanofibers. In typical embodiments, the electrode surface is comprisedof a conductive material (e.g., a metal, a semiconducting material, apolymer, a resin, etc.). In some, but not all, preferred embodiments,the electrode surface and/or the nanofibers of the electrode surface arecomprised of silicon. While in some embodiments the electrode surfaceand its nanofibers are of the same material (e.g., silicon, etc.), inother embodiments the surface and the nanofibers are of differentmaterials from one another. Additionally, while the nanofibers areoptionally grown in place upon the electrode surface, they are alsooptionally grown upon a different surface and subsequentlyplaced/attached to the electrode surface.

In other embodiments of the invention, the capacitor also comprises adielectric of a nonconductive material which covers substantially allmembers of the plurality of nanofibers (and the electrode surface onwhich the nanofibers exist). The dielectric, thus, exists between theelectrode surfaces (or “electrode plates” or the like) of the capacitor.Such dielectric can optionally be composed of one or more of a number ofmaterials, e.g., oxides, nitrides, various nonconductive polymers,ceramics, resins, porcelains, mica containing materials, glass, vacuum,rare earth oxides, gas (e.g., air, inert gases, etc.), or other typicaldielectrics used in electronic capacitors. Those of skill in the art arequite familiar with a broad range of materials used as dielectrics andcapable of use as dielectrics in the current invention. In someembodiments, the dielectric comprises a grown oxide layer and/or anaturally occurring oxide layer. The dielectric can comprise, e.g., ametal oxide such as aluminum oxide or tantalum oxide, etc. Thedielectric can also comprise silicon oxide.

In various embodiments, the dielectric, e.g., oxide layer, comprises adesired thickness (depending upon, e.g., the desired capacitance andother parameters such material construction, etc.). For example, thedielectric, e.g., oxide layer, can comprise a thickness from about 1 nmor less to about 1 um, from about 2 nm or less to about 750 nm, fromabout 5 nm or less to about 500 nm, from about 10 nm or less to about250 nm, or from about 50 nm or less to about 100 um. The dielectric,e.g., oxide layer, can also comprise a thickness that is substantiallyequivalent to the thickness of the electrode surface(s).

In typical embodiments, the capacitors herein also comprise a secondelectrode surface. Such second surface can comprise, e.g., a layer ofmaterial deposed upon the dielectric which covers the plurality ofnanofibers and the first electrode surface. In such embodiments, thesecond surface material can comprise a conductive material (e.g.,similar to the optional composition of the first electrode surface suchas a metal, a semiconducting material, a polymer, a resin, etc.). Invarious embodiments, the two electrode surfaces can be of the samecomposition, or can be of different composition. In some embodiments,the second surface comprises an evaporated or sputtered electricallyconducting material. Such evaporated/sputtered materials can include,e.g., aluminum, tantalum, platinum, nickel, a semiconducting material,polysilicon, titanium, titanium oxide, an electrolyte, gold, etc.

The various embodiments of capacitors herein can have a number ofdifferent densities of nanofibers per unit area outline (i.e., perfootprint area). For example, the density of the members of theplurality of nanofibers can range from about 0.11 nanofiber per squaremicron or less to at least about 1000 nanofibers per square micron, fromabout 1 nanofiber per square micron or less to at least about 500nanofibers per square micron, from about 10 nanofibers per square micronor less to at least about 250 nanofibers per square micron, or fromabout 50 nanofibers per square micron or less to at least about 100nanofibers per square micron.

Also, in various embodiments (e.g., in those wherein the nanostructurescomprise nanofibers, nanowires, or the like as opposed to nanocrystal orother similar nanostructures whose structural profile is notsubstantially cylindrical or tubular), the length of the members of theplurality of nanofibers can optionally range from about 1 micron or lessto at least about 500 microns, from about 5 micron or less to at leastabout 150 microns, from about 10 micron or less to at least about 125microns, or from about 50 micron or less to at least about 100 microns;and wherein the diameter of the members of the plurality of nanofibersranges from about 5 nm or less to at least about 1 micron, from about 10nm or less to at least about 500 nm, from about 20 nm or less to atleast about 250 nm, from about 20 nm or less to at least about 200 nm,from about 40 nm or less to at least about 200 nm, from about 50 nm orless to at least about 150 nm, or from about 75 nm or less to at leastabout 100 nm.

In yet other embodiments, the capacitors of the invention can comprisean electrode surface that, because of the nanofibers present, isconsiderably greater in surface area than other typical electrodesurfaces of similar or substantially equal footprint. For example, thedensity of the members of the plurality of nanofibers can optionallyincrease the surface area of the electrode surface from at least 1.5times to at least 100,00 times or more, at least 5 times to at least75,000 times or more, at least 10 times to at least 50,000 times ormore, at least 50 times to at least 25,000 times or more, at least 100times to at least 10,000 times or more, or at least 500 times to atleast 1,000 times or more, greater, in comparison to an area ofsubstantially equal footprint of an electrode surface withoutnanofibers.

Additionally, in other embodiments, the capacitors of the invention cancomprise a farad capacity that, because of the nanofibers present, isconsiderably greater in amount than that of other typical electrodesurfaces of similar or substantially equal footprint. For example, thefarad capacity of the capacitors of the invention can comprise fromabout at least 1.5 times to at least 100,00 times or more, at least 5times to at least 75,000 times or more, at least 10 times to at least50,000 times or more, at least 50 times to at least 25,000 times ormore, at least 100 times to at least 10,000 times or more, or at least500 times to at least 1,000 times or more greater capacitance than acapacitor having an electrode surface of substantially equal footprintbut not comprising a plurality of nanofibers.

In yet other aspects, the invention comprises a device which comprisesany of the capacitors of the invention. For example, timepieces, remotecontrols, medical devices, radios, computers, electronic equipment, etc.which have a capacitor herein are also aspects of the invention.

These and other objects and features of the invention will become morefully apparent when the following detailed description is read inconjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, Displays a schematic diagram of a generalized capacitor.

FIG. 2, Displays a schematic diagram representing an enhanced surfacearea capacitor.

FIG. 3, Panels A and B, Display photomicrographs of enhanced surfacearea substrates such as can form the basis for enhanced surface areacapacitors.

FIG. 4, Displays a graph comparing the surface area of a nanofiberenhanced area against varying distances between nanofibers.

DETAILED DESCRIPTION

The current invention comprises a number of different embodimentsfocused on nanofiber enhanced area surface substrates and uses thereofin capacitors. As will be apparent upon examination of the presentspecification, figures, and claims, substrates having such enhancedsurface areas present improved and unique capacitance aspects that arebeneficial in a wide variety of applications ranging from materialsscience to medical use and beyond. It will be appreciated that enhancedsurface areas herein are sometimes labeled as “nanofiber enhancedsurface areas” or, alternatively depending upon context, as “nanowireenhanced surface areas,” etc.

A common factor in the embodiments is the special morphology ofnanofiber surfaces (typically silicon oxide nanowires herein, but alsoencompassing other compositions and forms). For example, the vastlyincreased surface area presented by such substrates is utilized in,e.g., creation of improved capacitors for a wide variety of uses. Inmost aspects herein, it is thought that such benefits accrue from theunique morphology of the nanofiber surfaces (especially form the vastlyincreased surface area), but the various embodiments herein are notnecessarily limited by such theory in their construction, use, orapplication. In some embodiments, the nanofibers are optionallyfunctionalized with one or more entity.

Again, without being bound to a particular theory or mechanism ofoperation, the concept of the majority of benefits of the invention isbelieved to operate, at least in part, on the principle that thenanofiber surfaces herein present a greatly enhanced surface area inrelation to the same footprint area without nanofibers.

Capacitors

Capacitors, in general and in specific applications, are quite wellknown in the art. Various types of capacitors, e.g., electrolyticcapacitors, are replete throughout the literature. FIG. 1 shows thebasic components of a capacitor in a generalized fashion. In typicalcapacitors, a dielectric material is layered between two conductiveelectrodes (typically metal). An electrical charge proportional to thevoltage can then be stored in the capacitor when a voltage is appliedacross the electrodes. Thus, in FIG. 1, electrodes 100 and 200(alternately termed “electrode plates,” “electrode surfaces,” or“opposing plates” or the like) are separated by dielectric, 300. Theelectrodes are typically electrically connected to other components viaconnections such as 400. The capacitance “C” of a parallel-platecapacitor is given by Equation 1.

Equation  1:                                      $C = {\frac{{\, E_{\;_{0}}}K_{d}A}{d}.}$In Equation 1, “A” represents the area of the two plates in thecapacitor, while “E₀” represents the dielectric permittivity of vacuumor free space (8.85×10–12 F/m). “K_(d)” represents the dielectricconstant of the dielectric and “d” is the distance between the twoplates of the capacitor. As can be seen, capacitance depends upon thethickness of the dielectric (e.g., the distance between the electrodes),the dielectric constant of the dielectric, and the area (or effectivearea) of contact between the plates of the capacitor. Thus, greatercapacitance can be achieved through, e.g., increasing the dielectricconstant of the dielectric (e.g., by choosing a particular dielectricmaterial), increasing the electrode surface areas (e.g., by making theelectrode plates larger, etc.), decreasing the distance between theelectrodes, or combinations thereof. As described below, a number oftraditional capacitors (e.g., electrolytic capacitors) optimizecapacitance by etching/roughening the surface of the electrode toincrease the surface area “A.”

It will be appreciated that choice of dielectric material is aneffective means of manipulating the qualities of capacitors. Forexample, metal oxides can be used as materials for dielectrics. In otherwords, specific oxides are based upon the composition of the electrodeplates in the capacitor, e.g., aluminum oxides as dielectrics uponaluminum electrode plates, etc. In many capacitors, aluminum oxide andtantalum oxide (typically tantalum pentoxide) are often chosen. Thus, inmany types of capacitors (typically electrolytic capacitors) differentmetals (e.g., tantalum, aluminum, zinc, niobium and zirconium) arecoated with an oxide through an electrochemical process. For example, athin layer or coating of Al₂O₃ (aluminum oxide) can be formed on analuminum electrode plate by placing the metal in the proper chemicalsolution and running an electric current through it. The thickness ofsuch oxide layers (e.g., less than a micrometer, etc.) can bemanipulated through changes in reaction conditions. The oxide layer thusformed, comprises the dielectric of the capacitor. Typical dielectricsmade of metal oxides can be quite effective in capacitors, and canwithstand extremely high fields without breakdown. Various arrangementsof such capacitors can be rectifying (typical) or non-rectifying (oftenconstructed with two opposing layers of oxidized material).

As an often related point, the thickness of the dielectric, which alsoinfluences the capacitance, see Equation 1, can depend upon the choiceof material for the dielectric. For example, oxide layers (e.g., metaloxide layers as described above) are quite thin. Those of skill in theart will be familiar with such thin oxide layers, e.g., from usage inelectrolytic capacitors, etc. Such thinness also increases thecapacitance in addition to the dielectric constant component/influenceof the dielectric material itself because the thinness/thickness of thedielectric is often the distance, or is effectively the distance,between the electrode plates.

Yet another method of modifying capacitance is through change of theeffective areas of the electrode plates. Those of skill in the art willbe quite familiar with various means used to increase such effectiveareas. For example, some capacitors have increased the surface area ofone or both of the electrode plates through, e.g., constructing theelectrode plates from activated carbon fibers, etching or sintering ofthe surfaces of the electrode plates (e.g., etching metal), etc. Forexample, etching (e.g., chemical etching with acids) can produce anincreased surface area 30–100 times greater than an unetched surface. Adielectric (e.g., a metal oxide) is then typically formed/placed overthe increased surface area. Those of skill in the art will beknowledgeable about such practices and their corresponding use inconstruction of capacitors.

Once the surface area electrode has been covered with a dielectric, theopposing electrode can touch, or effectively touch, the dielectric. Forexample, a wet electrolytic solution can exist between the dielectric(touching and filling the surface variations) and the opposingelectrode. Dry electrolytic material can also fulfill a similar role. Ineither case, the solutions between the dielectric and the opposingelectrode, in effect, become extensions/part of the opposing electrode.

Nanofiber-Enhanced Capacitors

The capacitors of the present invention provide large capacitance valuesper footprint area of electrode plate, thus, allowing construction ofquite small and/or quite powerful capacitors. The capacitors herein haveone or more electrode plate which comprises nanofiber surfaces. Asexplained below, such nanofiber surfaces can optionally encompass myriadnanostructures (e.g., nanowires, nanorods, nanocrystals, etc.) whichvastly increase the surface area of the electrode plates. As explainedabove, increasing the surface area of the electrodes in a capacitorincreases its capacitance.

FIG. 2 displays a schematic diagram illustrating one possible embodimentof the current invention. As seen in FIG. 2, an electrode plate, 200,comprises a number of nanofibers, 230, upon it. In preferredembodiments, such nanofibers and electrode plate are “coated” with adielectric, 220, (e.g., typically an oxide layer), which dielectric isthen “coated” with another material to form the second, or opposing,electrode plate, 210.

In typical embodiments, the surface of the electrode plate (e.g., thearea between nanofiber attachments) is comprised of a conductivematerial (e.g., typically a metal, a semiconducting material, anelectrically conductive polymer or resin, etc.). Additionally, thenanofibers themselves are preferably comprised of electricallyconductive material(s) such as, e.g., metals, semiconducting materials,electrically conductive polymers, resins, etc. The electrode platesurface and/or the nanofibers on the plate are optionally comprised ofsilicon or silicon compounds. No matter the exact composition of thenanofibers and the rest of the body of the electrode plate, suchfeatures (i.e., the nanofibers and the plate surface) can optionally becomprised of the same material or can optionally be comprised ofdifferent materials. For example, the nanofibers can optionally comprisesilicon/silicon compounds while the electrode plate can optionallycomprise an electrically conductive metal. The possible difference incomposition between the nanofibers and the plate surface can arise,e.g., because the plurality of nanofibers can optionally be grown upon adifferent surface, harvested, and then deposited/attached to theelectrode plate surface.

Also, as can be seen in FIG. 2, capacitors of the invention comprise adielectric that typically “coats” the nanofiber surface of the electrodeplate. Thus, the dielectric closely conforms to the shape of thenanofibers and the electrode plate, in effect, forming a coating overthem. The dielectric typically coats or covers substantially allnanofibers and/or all areas of the electrode plate which comprises thenanofibers.

In many embodiments, the dielectric comprises an oxide layer, typicallyan oxide of the material(s) which form the nanofibers/electrode plate.For example, in some embodiments herein the dielectric comprises asilicon oxide layer coating the nanofibers/electrode plate. In yet otherembodiments, the dielectric is one or more of: an oxide, a nitride, apolymer, a ceramic, a resin, a porcelain, a mica containing material, aglass, vacuum, a rare earth oxide, a gas, etc. Those of skill in the artwill be familiar with other typical dielectrics used in electroniccapacitors and which are capable of use in the present invention. In anycase, as with typical capacitors, the dielectric in the presentinvention consists of a nonconductive material.

In embodiments wherein the dielectric comprises an oxide layer, suchlayer can be, e.g., a grown oxide layer or a naturally occurring oxidelayer. Again, typical oxide layers herein comprise silicon oxides. Thoseof skill in the art will also be aware of methods of manipulatingthickness and other growth/construction aspects of such oxide layers inorder to achieve the desired dielectric parameters. For example,particular environmental conditions present during thegrowth/construction of oxide layers can influence the thickness of theoxide layer, etc.

In various embodiments, the dielectric (e.g., the oxide layer) comprisesa thickness of from about 1 nm or less to about 1 um, from about 2 nm orless to about 750 nm, from about 5 nm or less to about 500 nm, fromabout 10 nm or less to about 250 nm, or from about 50 nm or less toabout 100 um. In yet other embodiments, the thickness is substantiallyequivalent to the thickness of the electrode surface comprising thenanofibers.

In typical embodiments herein, the capacitor comprises a secondelectrode plate, i.e., an opposing electrode plate that is on theopposite side of the dielectric than the electrode plate comprising thenanofiber surface. In preferred embodiments, this second electrode platecomprises a layer of material deposed upon the dielectric (i.e.,covering the plurality of nanofibers on the first electrode plate). See,e.g., FIG. 2. As with typical capacitors, the second electrode plate isalso electrically conductive, e.g., is composed of electricallyconductive material(s) such as metals, semiconducting materials,conductive polymers, conductive resins, etc. In order to achieve theclose mating between the second electrode plate and the complexnanofiber surface (i.e., coated with the dielectric), the secondelectrode plate is preferably evaporated or sputtered onto thedielectric. For example, an electrically conductive metal (e.g.,aluminum, tantalum, platinum, titanium, nickel, gold, etc.), asemiconducting material, polysilicon, titanium oxide, or an electrolyte,etc. can be used as the material of the second electrode plate. In someembodiments, the second electrode plate can optionally comprise anelectrolytic solution (either liquid or non-liquid) which, in effect,acts as the second electrode plate. Those of skill in the art will befamiliar with similar electrolytic set-ups from traditional electrolyticcapacitors, etc.

In the various embodiments herein, the capacitors (i.e., the electrodeplates comprising the nanofiber surfaces) can have various densities ofnanofibers within footprint areas. For example, some embodimentscomprise nanofiber densities of from about 0.11 nanofiber per squaremicron or less to at least about 1000 nanofibers per square micron, fromabout 1 nanofiber per square micron or less to at least about 500nanofibers per square micron, from about 10 nanofibers per square micronor less to at least about 250 nanofibers per square micron, or fromabout 50 nanofibers per square micron or less to at least about 100nanofibers per square micron.

Also, in different embodiments herein, the length of the nanofiberswithin the capacitors can be of different lengths. For example, thelength of the nanofibers herein can range from about 1 micron or less toat least about 500 microns, from about 5 micron or less to at leastabout 150 microns, from about 10 micron or less to at least about 125microns, or from about 50 micron or less to at least about 100 microns.Also, such various embodiments can comprise nanofibers of variousdiameters as well. Thus, different embodiments can comprise nanofibersthat range in diameter from about 5 nm or less to at least about 1micron, from about 10 nm or less to at least about 500 nm, from about 20nm or less to at least about 250 nm, from about 20 nm or less to atleast about 200 nm, from about 40 nm or less to at least about 200 nm,from about 50 nm or less to at least about 150 nm, or from about 75 nmor less to at least about 100 nm.

In the capacitors herein, the addition of the nanofibers to theelectrode surface can increase the surface area of the electrode surface(in comparison to an electrode surface which does not have nanofibers)by at least 1.5 times to at least 100,00 times or more, by at least 5times to at least 75,000 times or more, by at least 10 times to at least50,000 times or more, by at least 50 times to at least 25,000 times ormore, by at least 100 times to at least 10,000 times or more, or by atleast 500 times to at least 1,000 times or more. Such comparisons aretypically made by comparing similar “footprints” of electrode plates,i.e., similar or substantially similar area outlines.

An example of the increase in effective area of an electrode plate ofthe invention can be seen in FIG. 4. The graph in FIG. 4 compares thesurface area of a nanofiber enhanced area against the distance betweenthe nanofibers on the area. Thus, 10 nm nanowires with a 2 nmaluminum/aluminum oxide coating that are stacked 10 nm apart wouldproduce a surface area that would be ten times greater than any surfacereported in the literature.

Also, within the capacitors herein, addition of nanofibers to theelectrode surface/plate can increase the farad capacity of the capacitorby about at least 1.5 times to at least 100,00 times or more, by atleast 5 times to at least 75,000 times or more, by at least 10 times toat least 50,000 times or more, by at least 50 times to at least 25,000times or more, by at least 100 times to at least 10,000 times or more,or by at least 500 times to at least 1,000 times or more in relation toa capacitor which does not comprise a nanofiber enhanced surface. Again,such comparisons are typically made against similar or substantiallysimilar footprint or outline areas.

The current invention also includes devices comprising capacitors withnanofiber enhanced surfaces (i.e., typically nanofiber enhancedelectrode plates). Myriad examples of such devices can be contemplated.Those of skill in the art will appreciate the wide range of devicescapable of comprising/utilizing these capacitors. Basically, any devicerequiring a capacitor (especially a capacitor of large farad capabilityand small size) can comprise/utilize the current invention. Nonlimitingexamples of such devices can include, e.g., timepieces, watches, radios,remote controls, nanodevices, medical implant devices (e.g., pacemakers,prosthetic devices with electrical components, etc.), flow throughcapacitors, e.g., for water purification or solute sorting/separation.

Characteristics of Nanofiber Surface Substrates

As noted previously, increased surface area is a property that is soughtafter in many fields (e.g., in substrates for assays or separationcolumn matrices) as well as the current capacitors. For example, fieldssuch as tribology and those involving separations and adsorbents arequite concerned with maximizing surface areas. Other inventions by theinventor and coworkers have focused on such applications. See, e.g.,NANOFIBER SURFACES FOR USE IN ENHANCED SURFACE AREA APPLICATIONS, U.S.Ser. No. 10/792,402, filed Mar. 2, 2004. The current invention offerscapacitors, and applications of such, having surfaces that are increasedor enhanced with nanofibers (i.e., increased or enhanced in area inrelation to structures or surfaces without nanofibers, such as “planar”surfaces).

A “nanofiber enhanced surface area” or a capacitor or capacitorelectrode surface with an “enhanced surface area,” etc. hereincorresponds to a capacitor or capacitor electrode surface comprising aplurality of nanofibers (e.g., nanowires, nanotubes, nanospheres, etc.)attached to a substrate so that the surface area within a certain“footprint” of the substrate is increased relative to the surface areawithin the same footprint without the nanofibers. Such footprintcorresponds to outlining the parameters of the measurement area.

As explained in greater detail below, in typical embodiments herein, thenanofibers (and often the electrode surface substrate) are composed ofsilicon and/or silicon oxides. It will be noted that such compositionsconvey a number of benefits in certain embodiments herein. Also, in someembodiments herein, one or more of the plurality of nanofibers isfunctionalized with one or more moiety. See, below. However, it shouldalso be noted that the current invention is not specifically limited bythe composition of the nanofibers or of the substrate or of anyfunctionalization, unless otherwise noted.

Thus, as an illustrative, but not limiting, example, FIGS. 2 and 3present schematic and actual representations of nanofiber enhancedsurface area substrates of the invention, such as would be constructedwithin capacitors herein. FIG. 2 shows a schematic of a nanofibercapacitor. FIG. 3 displays photomicrographs of an enhanced surface areananofiber substrate such as would form the basis for a nanofiber plateelement. It will be noted that the number and shape and distribution ofthe nanofibers allows ample opportunity for increased surface area, etc.Again, it is to be emphasized that such examples are merely toillustrate the myriad possible embodiments of the current invention.

The various embodiments of the current invention are adaptable to, anduseful for, a great number of different applications. For example, asexplained in more detail below, various permutations of the inventioncan be used in, e.g., any number of devices requiring capacitors. Otheruses and embodiments are examined herein.

As will be appreciated by those of skill in the art, in numerousmaterials the surface properties can optionally provide a great deal ofthe functionality or use of the material. For example, in variousembodiments, the adherence or coverage of the dielectric is provided byor aided by interaction of the nanofiber elements with appropriatefunctionalization moieties.

As also will be appreciated by those of skill in the art, many aspectsof the current invention are optionally variable (e.g., surfacechemistries on the nanofibers, surface chemistries on any end of thenanofibers or on the substrate surface, etc.). Specific illustration ofvarious modifications, etc. herein, should therefore not be taken asnecessarily limiting the current invention. Also, it will beappreciated, and is explained in more detail below, that the length tothickness ratio of the nanofibers herein is optionally varied, as is,e.g., the composition of the nanofibers and the dielectric. Furthermore,a variety of methods can be employed to bring the fibers in contact withsurfaces. Additionally, while some embodiments herein comprisenanofibers that are specifically functionalized in one or more ways,e.g., through attachment of moieties or functional groups to thenanofibers, other embodiments comprise nanofibers which are notfunctionalized.

Nanofibers and Nanofiber Construction

In typical embodiments herein the surfaces (i.e., the nanofiber enhancedarea surfaces) and the nanofibers themselves can optionally comprise anynumber of materials. The actual composition of the surfaces and thenanofibers is based upon a number of possible factors. Such factors caninclude, for example, the intended use of the enhanced area surfaces,e.g., the specific parameters such as amount of capacitance and/orcapacitance per unit area needed, the conditions under which they willbe used (e.g., temperature, pH, presence of light (e.g., UV),atmosphere, etc.), the durability of the surfaces and the cost, etc. Intypical and preferred embodiments the nanofibers are electricallyconductive. The ductility and breaking strength of nanowires will varydepending on, e.g., their composition. For example, ceramic ZnO wirescan be more brittle than silicon or glass nanowires, while carbonnanotubes may have a higher tensile strength.

As explained more fully below, some possible materials used to constructthe nanofibers and nanofiber enhanced surfaces herein, include, e.g.,silicon, ZnO, TiO, carbon, and carbon nanotubes. See below. Thenanofibers of the invention are also optionally coated orfunctionalized, e.g., to enhance or add specific properties. Forexample, polymers, ceramics or small molecules can optionally be used ascoating materials on the nanofibers, e.g., between the nanofibers andthe dielectric, etc. The optional coatings can impart characteristicssuch as water resistance, improved electrical properties, etc.Additionally, specific moieties or functional groups can also beattached to or associated with the nanofibers herein.

Of course, it will be appreciated that the current invention is notlimited by recitation of particular nanofiber and/or substratecompositions, and that, unless otherwise stated, any of a number ofother materials are optionally used in different embodiments herein.Additionally, the materials used to comprise the nanofibers canoptionally be the same as the material used to comprise the substratesurfaces or they can be different from the materials used to constructthe substrate surfaces.

In yet other embodiments herein, the nanofibers involved can optionallycomprise various physical conformations such as, e.g., nanotubules(e.g., hollow-cored structures), nanorods, nanocrystals, nanowhiskersetc. A variety of nanofiber types are optionally used in this inventionincluding carbon nanotubes, metallic nanotubes, metals and ceramics.Such nanostructures are all optionally used in increasing the surfacearea of the electrode surfaces, etc. While typical embodiments hereinrecite “nanofiber,” such language should not be construed as necessarilylimiting unless specified to be so.

It is to be understood that this invention is not limited to particularconfigurations, which can, of course, vary (e.g., different combinationsof nanofibers and substrates and optional moieties, etc. which areoptionally present in a range of lengths, densities, etc.). It is alsoto be understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to benecessarily limiting. As used in this specification and the appendedclaims, the singular forms “a,” “an” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a nanofiber” optionally includes a plurality of suchnanofibers, and the like. Unless defined otherwise, all scientific andtechnical terms are understood to have the same meaning as commonly usedin the art to which they pertain. For the purpose of the presentinvention, additional specific terms are defined throughout.

A) Nanofibers

The term “nanofiber” as used herein, refers to a nanostructure typicallycharacterized by at least one physical dimension less than about 1000nm, less than about 500 nm, less than about 250 nm, less than about 150nm, less than about 100 nm, less than about 50 nm, less than about 25 nmor even less than about 10 nm or 5 nm. In many cases, the region orcharacteristic dimension will be along the smallest axis of thestructure.

Nanofibers of this invention typically have one principle axis that islonger than the other two principle axes and, thus, have an aspect ratiogreater than one, an aspect ratio of 2 or greater, an aspect ratiogreater than about 10, an aspect ratio greater than about 20, or anaspect ratio greater than about 100, 200, or 500. In certainembodiments, nanofibers herein have a substantially uniform diameter. Insome embodiments, the diameter shows a variance less than about 20%,less than about 10%, less than about 5%, or less than about 1% over theregion of greatest variability and over a linear dimension of at least 5nm, at least 10 nm, at least 20 nm, or at least 50 nm. For example, awide range of diameters could be desirable due to cost considerationsand/or to create a more random surface. Typically the diameter isevaluated away from the ends of the nanofiber (e.g. over the central20%, 40%, 50%, or 80% of the nanofiber). In yet other embodiments, thenanofibers herein have a non-uniform diameter (i.e., they vary indiameter along their length). Also in certain embodiments, thenanofibers of this invention are substantially crystalline and/orsubstantially monocrystalline.

Once again, it will be appreciated that the term nanofiber, canoptionally include such structures as, e.g., nanowires, nanowhiskers,semi-conducting nanofibers, carbon nanotubes or nanotubules and thelike.

The nanofibers of this invention can be substantially homogeneous inmaterial properties, or in certain embodiments they are heterogeneous(e.g. nanofiber heterostructures) and can be fabricated from essentiallyany convenient material or materials. The nanofibers can comprise “pure”materials, substantially pure materials, doped materials and the likeand can include, in various combinations, insulators, conductors, andsemiconductors. Additionally, while some illustrative nanofibers hereinare comprised of silicon (or silicon oxides), as explained above, theyoptionally can be comprised of any of a number of different materials,unless otherwise stated.

Composition of nanofibers can vary depending upon a number of factors,e.g., specific functionalization (if any) to be associated with orattached to the nanofibers, durability, cost, conditions of use, etc.The composition of nanofibers is quite well known to those of skill inthe art. As will be appreciated by such skilled persons, the nanofibersof the invention can, thus, be composed of any of a myriad of possiblesubstances (or combinations thereof). Some embodiments herein comprisenanofibers composed of one or more organic or inorganic compound ormaterial. Any recitation of specific nanofiber compositions hereinshould not be taken as necessarily limiting.

Additionally, the nanofibers of the invention are optionally constructedthrough any of a number of different methods, and examples listed hereinshould not be taken as necessarily limiting. Thus, nanofibersconstructed through means not specifically described herein, but whichfall within the parameters as set forth herein are still nanofibers ofthe invention and/or are used with the devices and methods of theinvention.

In a general sense, the nanofibers of the current invention often (butnot exclusively) comprise long thin protuberances (e.g., fibers,nanowires, nanotubules, etc.) grown from a solid, optionally planar,substrate. Of course, in some embodiments herein, the fibers aredetached from the substrate on which they are grown and attached to asecond substrate. The second substrate need not be planar and, in fact,can comprise a myriad of three-dimensional conformations, as can thesubstrate on which the nanofibers were grown originally. In someembodiments herein, the substrates are flexible. Also, as explained ingreater detail below, nanofibers of the invention can begrown/constructed in, or upon, variously configured surfaces, e.g., on aflat substrate that is rolled into an overlapping cylinder, etc. Seeinfra.

In various embodiments herein, the nanofibers involved are optionallygrown on a first substrate and then subsequently transferred to a secondsubstrate which is to have the enhanced surface area. Such embodimentsare particularly useful in situations wherein the substrate desiredneeds to be flexible or conforming to a particular three dimensionalshape that is not readily subjected to direct application or growth ofnanofibers thereon. For example, nanofibers can be grown on such rigidsurfaces as, e.g., silicon wafers or other similar substrates. Thenanofibers thus grown can then optionally be transferred to a flexiblebacking. Again, it will be appreciated, however, that the invention isnot limited to particular nanofiber or substrate compositions. Forexample, nanofibers are optionally gown on any of a variety of differentsurfaces, including, e.g., flexible foils such as aluminum or the like.Additionally, for high temperature growth processes, any metal, ceramicor other thermally stable material is optionally used as a substrate onwhich to grow nanofibers of the invention. Furthermore, low temperaturesynthesis methods such as solution phase methods can be utilized inconjunction with an even wider variety of substrates on which to grownanofibers. For example, flexible polymer substrates and other similarsubstances are optionally used as substrates for nanofibergrowth/attachment.

As one example, the growth of nanofibers on a surface using a goldcatalyst has been demonstrated in the literature. Applications targetedfor such fibers are based on harvesting them from the substrate and thenassembling them into devices. However, in many other embodiments herein,the nanofibers involved in enhanced surface areas are grown in place.Available methods, such as growing nanofibers from gold colloidsdeposited on surfaces are, thus, optionally used herein. The end productwhich results is the substrate upon which the fibers are grown (i.e.,with an enhanced surface area due to the nanofibers). As will beappreciated, specific embodiments and uses herein, unless statedotherwise, can optionally comprise nanofibers grown in the place oftheir use and/or through nanofibers grown elsewhere, which are harvestedand transferred to the place of their use. For example, many embodimentsherein relate to leaving the fibers intact on the growth substrate andtaking advantage of the unique properties the fibers impart on thesubstrate. Other embodiments relate to growth of fibers on a firstsubstrate and transfer of the fibers to a second substrate to takeadvantage of the unique properties that the fibers impart on the secondsubstrate.

For example, if nanofibers of the invention were grown on, e.g., anon-flexible substrate (e.g., such as some types of silicon wafers) theycould be transferred from such non-flexible substrate to a flexiblesubstrate (e.g., such as a conductive flexible metallic material).Again, as will be apparent to those of skill in the art, the nanofibersherein could optionally be grown on a flexible substrate to start with,but different desired parameters may influence such decisions.

A variety of methods may be employed in transferring nanofibers from asurface upon which they are fabricated to another surface. For example,nanofibers may be harvested into a liquid suspension, e.g., ethanol,which is then coated onto another surface. Additionally, nanofibers froma first surface (e.g., ones grown on the first surface or which havebeen transferred to the first surface) can optionally be “harvested” byapplying a sticky coating or material to the nanofibers and then peelingsuch coating/material away from the first surface. The stickycoating/material is then optionally placed against a second surface todeposit the nanofibers. Examples of sticky coatings/materials which areoptionally used for such transfer include, but are not limited to, e.g.,tape (e.g., 3M Scotch® tape), magnetic strips, curing adhesives (e.g.,epoxies, rubber cement, etc.), etc. The nanofibers could be removed fromthe growth substrate, mixed into a plastic, and then surface of suchplastic could be ablated or etched away to expose the fibers.

The actual nanofiber constructions of the invention are optionallycomplex. For example, FIG. 3 is a photomicrograph of a typical nanofiberconstruction. As can be seen in FIG. 3, the nanofibers form a complexthree-dimensional pattern. Possible interlacing and variable heights,curves, bends, etc. can form a surface which greatly increases thesurface area per unit substrate (e.g., as compared with a planar surfacewithout nanofibers). Of course, in other embodiments herein, it shouldbe apparent that the nanofibers need not be as complex as, e.g., thoseshown in FIG. 3. Thus, in many embodiments herein, the nanofibers are“straight” and do not tend to bend, curve, or curl. However, suchstraight nanofibers are still encompassed within the current invention.

B) Functionalization

Some embodiments of the invention comprise nanofiber and nanofiberenhanced area surfaces in which the fibers include one or morefunctional moiety (e.g., a chemically reactive group) attached to them.Functionalized nanofibers are optionally used in many differentembodiments, e.g., to confer increased electrical conductance to thenanofibers, to help the dielectric adhere/bond to the nanofibers, etc.Beneficially, typical embodiments of enhanced surface areas herein arecomprised of silicon oxides, which are conveniently modified with alarge variety of moieties. Of course, other embodiments herein arecomprised of other nanofiber compositions (e.g., polymers, ceramics,metals that are coated by CVD or sol-gel sputtering, etc.) which arealso optionally functionalized for specific purposes. Those of skill inthe art will be familiar with numerous functionalizations andfunctionalization techniques which are optionally used herein.

Further relevant information can be found in CRC Handbook of Chemistryand Physics (2003) 83^(rd) edition by CRC Press. Details on conductiveand other coatings, which can also be incorporated onto nanofibers ofthe invention by plasma methods and the like can be found in H. S. Nalwa(ed.), Handbook of Organic Conductive Molecules and Polymers, John Wiley& Sons 1997. See also, ORGANIC SPECIES THAT FACILITATE CHARGE TRANSFERTO/FROM NANOCRYSTALS U.S. Ser. No. 60/452,232 filed Mar. 4, 2003 byWhiteford et al. Additionally, details regarding relevant moiety andother chemistries, as well as methods for construction/use of such, canbe found, e.g., in Hermanson Bioconjugate Techniques Academic Press(1996), Kirk-Othmer Concise Encyclopedia of Chemical Technology (1999)Fourth Edition by Grayson et al. (ed.) John Wiley & Sons, Inc., New Yorkand in Kirk-Othmer Encyclopedia of Chemical Technology Fourth Edition(1998 and 2000) by Grayson et al. (ed.) Wiley Interscience (printedition)/John Wiley & Sons, Inc. (e-format). Details regarding organicchemistry, relevant for, e.g., coupling of additional moieties to afunctionalized surface of nanofibers can be found, e.g., in Greene(1981) Protective Groups in Organic Synthesis, John Wiley and Sons, NewYork, as well as in Schmidt (1996) Organic Chemistry Mosby, St Louis,Mo., and March's Advanced Organic Chemistry Reactions, Mechanisms andStructure, Fifth Edition (2000) Smith and March, Wiley Interscience NewYork ISBN 0-471-58589-0. Those of skill in the art will be familiar withmany other related references and techniques amenable forfunctionalization of the nanofibers herein.

Thus, again as will be appreciated, the substrates involved, thenanofibers involved (e.g., attached to, or deposited upon, thesubstrates), and any optional functionalization of the nanofibers and/orsubstrates, and the like can be varied. For example, the length,diameter, conformation and density of the fibers can be varied, as canthe composition of the fibers and their surface chemistry.

C) Density and Related Issues

In terms of density, it will be appreciated that by including morenanofibers emanating from a surface, one automatically increases theamount of surface area that is extended from the basic underlyingsubstrate. This, thus, increases the amount of intimate contact areabetween the surface and the dielectric and, indirectly, to the opposingelectrode plate coming into contact with the nanofiber surfaces. Asexplained in more detail below, the embodiments herein optionallycomprise a density of nanofibers on a surface of from about 0.1 to about1000 or more nanofibers per micrometer² of the substrate surface. Again,here too, it will be appreciated that such density depends upon factorssuch as the diameter of the individual nanofibers, etc. See, below. Thenanofiber density influences the enhanced surface area, since a greaternumber of nanofibers will tend to increase the overall amount of area ofthe surface. Therefore, the density of the nanofibers herein typicallyhas a bearing on the increased capacitance of the enhanced surface areamaterials because such density is a factor in the overall area of thesurface.

For example, a typical flat planar substrate, e.g., a silicon oxide chipor a glass slide, will typically comprise “x” surface area per squaremicron (i.e., within a square micron footprint). However, if such asubstrate surface were coated with nanofibers, then the availablesurface area would be much greater. In some embodiments herein eachnanofiber on a surface comprises about 1 square micron in surface area(i.e., the sides and tip of each nanofiber present that much surfacearea). If a comparable square micron of substrate comprised from 10 toabout 100 nanofibers per square micron, the available surface area isthus 10 to 100 times greater than a plain flat surface. Therefore, inthe current illustration, an enhanced surface area would have 10× to100× more surface area per square micron footprint. It will beappreciated that the density of nanofibers on a substrate is influencedby, e.g., the diameter of the nanofibers and any functionalization ofsuch fibers, etc.

Different embodiments of the invention comprise a range of suchdifferent densities (i.e., number of nanofibers per unit area of asubstrate to which nanofibers are attached). The number of nanofibersper unit area can optionally range from about 1 nanofiber per 10 micron²up to about 200 or more nanofibers per micron²; from about 1 nanofiberper micron² up to about 200 or more nanofibers per micron²; from about10 nanofibers per micron² up to about 100 or more nanofibers permicron²; or from about 25 nanofibers per micron² up to about 75 or morenanofibers per micron². In yet other embodiments, the density canoptionally range from about 1 to 3 nanowires per square micron to up toapproximately 2,500 or more nanowires per square micron.

In terms of individual fiber dimensions, it will be appreciated that byincreasing the thickness or diameter of each individual fiber one will,again, automatically increase the overall area of the fiber and, thus,the overall area of the substrate and, hence, the electrode plate. Thediameter of nanofibers herein can be controlled through, e.g., choice ofcompositions and growth conditions of the nanofibers, addition ofmoieties, coatings or the like, etc. Preferred fiber thicknesses areoptionally between from about 5 nm up to about 1 micron or more (e.g., 5microns); from about 10 nm to about 750 nanometers or more; from about25 nm to about 500 nanometers or more; from about 50 nm to about 250nanometers or more, or from about 75 nm to about 100 nanometers or more.In some embodiments, the nanofibers comprise a diameter of approximately40 nm.

In addition to diameter, surface area of nanofibers (and thereforesurface area of a substrate to which the nanofibers are attached and,thus, of the electrode plate) also is influenced by length of thenanofibers. Of course, it will also be understood that for some fibermaterials, increasing length may yield increasing fragility.Accordingly, preferred fiber lengths will typically be between about 2microns (e.g., 0.5 microns) up to about 1 mm or more; from about 10microns to about 500 micrometers or more; from about 25 microns to about250 microns or more; or from about 50 microns to about 100 microns ormore. Some embodiments comprise nanofibers of approximately 50 micronsin length. Some embodiments herein comprise nanofibers of approximately40 nm in diameter and approximately 50 microns in length.

Nanofibers herein can present a variety of aspect ratios. Thus,nanofiber diameter can comprise, e.g., from about 5 nm up to about 1micron or more (e.g., 5 microns); from about 10 nm to about 750nanometers or more; from about 25 nm to about 500 nanometers or more;from about 50 nm to about 250 nanometers or more, or from about 75 nm toabout 100 nanometers or more, while the lengths of such nanofibers cancomprise, e.g., from about 2 microns (e.g., 0.5 microns) up to about 1mm or more; from about 10 microns to about 500 micrometers or more; fromabout 25 microns to about 250 microns or more; or from about 50 micronsto about 100 microns or more.

Fibers that are, at least in part, elevated above a surface areparticularly preferred, e.g., where at least a portion of the fibers inthe fiber surface are elevated at least 10 nm, or even at least 100 nmabove a surface, in order to provide enhanced surface area available forcoating with a dielectric and the opposing electrode plate.

Again, as seen in FIG. 3, the nanofibers optionally form a complexthree-dimensional structure. The degree of such complexity depends inpart upon, e.g., the length of the nanofibers, the diameter of thenanofibers, the length:diameter aspect ratio of the nanofibers, moieties(if any) attached to the nanofibers, and the growth conditions of thenanofibers, etc. The bending, interlacing, etc. of nanofibers, whichhelp affect the degree of enhanced surface area available, areoptionally manipulated through, e.g., control of the number ofnanofibers per unit area as well as through the diameter of thenanofibers, the length and the composition of the nanofibers, etc. Thus,it will be appreciated that enhanced surface area of nanofibersubstrates herein is optionally controlled through manipulation of theseand other parameters.

Also, in some, but not all, embodiments herein, the nanofibers of theinvention comprise bent, curved, or even curled forms. As can beappreciated, if a single nanofiber snakes or coils over a surface (butis still just a single fiber per unit area bound to a first surface),the fiber can still provide an enhanced surface area due to its length,etc.

D) Nanofiber Construction

As will be appreciated, the current invention is not limited by themeans of construction of the nanofibers herein. For example, while someof the nanofibers herein are composed of silicon, the use of siliconshould not be construed as necessarily limiting. For example, a numberof other electrically conductive materials are optionally used. Theformation of nanofibers is possible through a number of differentapproaches that are well known to those of skill in the art, all ofwhich are amenable to embodiments of the current invention.

Typical embodiments herein can be used with existing methods ofnanostructure fabrication, as will be known by those skilled in the art,as well as methods mentioned or described herein. In other words, avariety of methods for making nanofibers and nanofiber containingstructures have been described and can be adapted for use in variousembodiments of the invention.

The nanofibers can be fabricated of essentially any convenientelectrically conductive material (e.g., a semiconducting material, aferroelectric material, a metal, ceramic, polymers, etc.) and cancomprise essentially a single material or can be heterostructures. Forexample, the nanofibers can comprise a semiconducting material, forexample a material comprising a first element selected from group 2 orfrom group 12 of the periodic table and a second element selected fromgroup 16 (e.g., ZnS, ZnO, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe,MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, andlike materials); a material comprising a first element selected fromgroup 13 and a second element selected from group 15 (e.g., GaN, GaP,GaAs, GaSb, InN, InP, InAs, InSb, and like materials); a materialcomprising a group 14 element (Ge, Si, and like materials); a materialsuch as PbS, PbSe, PbTe, AIS, AIP, and AlSb; or an alloy or a mixturethereof.

In some embodiments herein, the nanofibers are optionally comprised ofsilicon or a silicon oxide. It will be understood by one of skill in theart that the term “silicon oxide” as used herein can be understood torefer to silicon at any level of oxidation. Thus, the term silicon oxidecan refer to the chemical structure SiO_(x), wherein x is between 0 and2 inclusive. In other embodiments, the nanofibers can comprise, e.g.,silicon, glass, quartz, plastic, metal, polymers, TiO, ZnO, ZnS, ZnSe,ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe,CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, GaN, GaP, GaAs, GaSb, InN, InP,InAs, InSb, PbS, PbSe, PbTe, AIS, AlP, AlSb, SiO₁, SiO₂, siliconcarbide, silicon nitride, polyacrylonitrile (PAN), polyetherketone,polyimide, aromatic polymers, or aliphatic polymers that areelectrically conductive.

It will be appreciated that in some embodiments, the nanofibers cancomprise the same material as one or more substrate surface (i.e., asurface to which the nanofibers are attached or associated), while inother embodiments, the nanofibers comprise a different material than thesubstrate surface. Additionally, the substrate surfaces can optionallycomprise any one or more of the same materials or types of materials asdo the nanofibers (e.g., such as the materials illustrated herein).

As previously stated, some, but by no means all, embodiments hereincomprise silicon nanofibers. Common methods for making siliconnanofibers include vapor liquid solid growth (VLS), laser ablation(laser catalytic growth) and thermal evaporation. See, for example,Morales et al. (1998) “A Laser Ablation Method for the Synthesis ofCrystalline Semiconductor Nanowires” Science 279, 208–211 (1998). In oneexample approach a hybrid pulsed laser ablation/chemical vapordeposition (PLA-CVD) process for the synthesis of semiconductornanofibers with longitudinally ordered heterostructures, and variationsthereof can be used. See, Wu et al. (2002) “Block-by-Block Growth ofSingle-Crystalline Si/SiGe Superlattice Nanowires,” Nano Letters Vol. 0,No. 0.

In general, multiple methods of making nanofibers have been describedand can be applied in the embodiments herein. In addition to Morales etal. and Wu et al. (above), see, for example, Lieber et al. (2001)“Carbide Nanomaterials” U.S. Pat. No. 6,190,634 B1; Lieber et al. (2000)“Nanometer Scale Microscopy Probes” U.S. Pat. No. 6,159,742; Lieber etal. (2000) “Method of Producing Metal Oxide Nanorods” U.S. Pat. No.6,036,774; Lieber et al. (1999) “Metal Oxide Nanorods” U.S. Pat. No.5,897,945; Lieber et al. (1999) “Preparation of Carbide Nanorods” U.S.Pat. No. 5,997,832; Lieber et al. (1998) “Covalent Carbon NitrideMaterial Comprising C₂N and Formation Method” U.S. Pat. No. 5,840,435;Thess, et al. (1996) “Crystalline Ropes of Metallic Carbon Nanotubes”Science 273:483–486; Lieber et al. (1993) “Method of Making aSuperconducting Fullerene Composition By Reacting a Fullerene with anAlloy Containing Alkali Metal” U.S. Pat. No. 5,196,396; and Lieber etal. (1993) “Machining Oxide Thin Films with an Atomic Force Microscope:Pattern and Object Formation on the Nanometer Scale” U.S. Pat. No.5,252,835. One dimensional semiconductor heterostructure nanocrystals,have been described. See, e.g., Bjork et al. (2002) “One-dimensionalSteeplechase for Electrons Realized” Nano Letters Vol. 0, No. 0.

It should be noted that some references herein, while not specific tonanofibers, are typically still applicable to the invention. Forexample, background issues of construction conditions and the like areapplicable between nanofibers and other nanostructures (e.g.,nanocrystals, etc.). Also, while described generally in terms ofnanofibers and the like, again, it will be appreciated that nanospheres,nanocrystals, etc. are also optionally used to increase the surface areaand capacitance of the embodiments herein. See above.

In another approach which is optionally used to construct nanofibers ofthe invention, synthetic procedures to prepare individual nanofibers onsurfaces and in bulk are described, for example, by Kong, et al. (1998)“Synthesis of Individual Single-Walled Carbon Nanotubes on PatternedSilicon Wafers,” Nature 395:878–881, and Kong, et al. (1998) “ChemicalVapor Deposition of Methane for Single-Walled Carbon Nanotubes,” Chem.Phys. Lett. 292:567–574.

In yet another approach, substrates and self assembling monolayer (SAM)forming materials can be used, e.g., along with microcontact printingtechniques to make nanofibers, such as those described by Schon, Meng,and Bao, “Self-assembled monolayer organic field-effect transistors,”Nature 413:713 (2001); Zhou et al. (1997) “NanoscaleMetal/Self-Assembled Monolayer/Metal Heterostructures,” Applied PhysicsLetters 71:611; and WO 96/29629 (Whitesides, et al., published Jun. 26,1996).

In some embodiments herein, nanofibers can be synthesized using ametallic catalyst. A benefit of such embodiments allows use of uniquematerials suitable for surface modifications to create enhancedproperties. A unique property of such nanofibers is that they are cappedat one end with a catalyst, typically gold. This catalyst end canoptionally be functionalized using, e.g., thiol chemistry withoutaffecting the rest of the fiber, thus, making it capable of bonding toan appropriate surface. In such embodiments, the result of suchfunctionalization, etc., is to make a surface with end-linkednanofibers. These resulting “fuzzy” surfaces, therefore, have increasedsurface areas (i.e., in relation to the surfaces without the nanofibers)and other unique properties. In some such embodiments, the surface ofthe nanofiber and/or the target substrate surface is optionallychemically modified (typically, but not necessarily, without affectingthe gold tip) in order to give a wide range of properties useful in manyapplications.

In other embodiments, to increase or enhance a surface area, thenanofibers are optionally laid “flat” (i.e., substantially parallel tothe substrate surface) by chemical or electrostatic interaction onsurfaces, instead of end-linking the nanofibers to the substrate. In yetother embodiments herein, techniques involve coating the base surfacewith functional groups which repel the polarity on the nanofiber so thatthe fibers do not lay on the surface but are end-linked.

Synthesis of nanostructures, e.g., nanocrystals, of various compositionis described in, e.g., Peng et al. (2000) “Shape control of CdSenanocrystals” Nature 404:59–61; Puntes et al. (2001) “Colloidalnanocrystal shape and size control: The case of cobalt” Science291:2115–2117; U.S. Pat. No. 6,306,736 to Alivisatos et al. (Oct. 23,2001) entitled “Process for forming shaped group III-V semiconductornanocrystals, and product formed using process”; U.S. Pat. No. 6,225,198to Alivisatos et al. (May 1, 2001) entitled “Process for forming shapedgroup II-VI semiconductor nanocrystals, and product formed usingprocess”; U.S. Pat. No. 5,505,928 to Alivisatos et al. (Apr. 9, 1996)entitled “Preparation of III-V semiconductor nanocrystals”; U.S. Pat.No. 5,751,018 to Alivisatos et al. (May 12, 1998) entitled“Semiconductor nanocrystals covalently bound to solid inorganic surfacesusing self-assembled monolayers”; U.S. Pat. No. 6,048,616 to Gallagheret al. (Apr. 11, 2000) entitled “Encapsulated quantum sized dopedsemiconductor particles and method of manufacturing same”; and U.S. Pat.No. 5,990,479 to Weiss et al. (Nov. 23, 1999) entitled “Organoluminescent semiconductor nanocrystal probes for biological applicationsand process for making and using such probes.”

Additional information on growth of nanofibers, such as nanowires,having various aspect ratios, including nanofibers with controlleddiameters, is described in, e.g., Gudiksen et al. (2000)“Diameter-selective synthesis of semiconductor nanowires” J. Am. Chem.Soc. 122:8801–8802; Cui et al. (2001) “Diameter-controlled synthesis ofsingle-crystal silicon nanowires” Appl. Phys. Lett. 78:2214–2216;Gudiksen et al. (2001) “Synthetic control of the diameter and length ofsingle crystal semiconductor nanowires” J. Phys. Chem. B 105:4062–4064;Morales et al. (1998) “A laser ablation method for the synthesis ofcrystalline semiconductor nanowires” Science 279:208–211; Duan et al.(2000) “General synthesis of compound semiconductor nanowires” Adv.Mater. 12:298–302; Cui et al. (2000) “Doping and electrical transport insilicon nanowires” J. Phys. Chem. B 104:5213–5216; Peng et al. (2000),supra; Puntes et al. (2001), supra; U.S. Pat. No. 6,225,198 toAlivisatos et al., supra; U.S. Pat. No. 6,036,774 to Lieber et al. (Mar.14, 2000) entitled “Method of producing metal oxide nanorods”; U.S. Pat.No. 5,897,945 to Lieber et al. (Apr. 27, 1999) entitled “Metal oxidenanorods”; U.S. Pat. No. 5,997,832 to Lieber et al. (Dec. 7, 1999)“Preparation of carbide nanorods”; Urbau et al. (2002) “Synthesis ofsingle-crystalline perovskite nanowires composed of barium titanate andstrontium titanate” J. Am. Chem. Soc., 124:1186; Yun et al. (2002)“Ferroelectric Properties of Individual Barium Titanate NanowiresInvestigated by Scanned Probe Microscopy” Nano Letters 2, 447; andpublished PCT application nos. WO 02/17362, and WO 02/080280.

Growth of branched nanofibers (e.g., nanotetrapods, tripods, bipods, andbranched tetrapods) is described in, e.g., Jun et al. (2001) “Controlledsynthesis of multi-armed CdS nanorod architectures using monosurfactantsystem” J. Am. Chem. Soc. 123:5150–5151; and Manna et al. (2000)“Synthesis of Soluble and Processable Rod-, Arrow-, Teardrop-, andTetrapod-Shaped CdSe Nanocrystals” J. Am. Chem. Soc. 122:12700–12706.Synthesis of nanoparticles is described in, e.g., U.S. Pat. No.5,690,807 to Clark Jr. et al. (Nov. 25, 1997) entitled “Method forproducing semiconductor particles”; U.S. Pat. No. 6,136,156 to El-Shall,et al. (Oct. 24, 2000) entitled “Nanoparticles of silicon oxide alloys”;U.S. Pat. No. 6,413,489 to Ying et al. (Jul. 2, 2002) entitled“Synthesis of nanometer-sized particles by reverse micelle mediatedtechniques”; and Liu et al. (2001) “Sol-Gel Synthesis of Free-StandingFerroelectric Lead Zirconate Titanate Nanoparticles” J. Am. Chem. Soc.123:4344. Synthesis of nanoparticles is also described in the abovecitations for growth of nanocrystals, and nanofibers such as nanowires,branched nanowires, etc.

Synthesis of core-shell nanofibers, e.g., nanostructureheterostructures, is described in, e.g., Peng et al. (1997) “Epitaxialgrowth of highly luminescent CdSe/CdS core/shell nanocrystals withphotostability and electronic accessibility” J. Am. Chem. Soc.119:7019–7029; Dabbousi et al. (1997) “(CdSe)ZnS core-shell quantumdots: Synthesis and characterization of a size series of highlyluminescent nanocrystallites” J. Phys. Chem. B 101:9463–9475; Manna etal. (2002) “Epitaxial growth and photochemical annealing of gradedCdS/ZnS shells on colloidal CdSe nanorods” J. Am. Chem. Soc.124:7136–7145; and Cao et al. (2000) “Growth and properties ofsemiconductor core/shell nanocrystals with InAs cores” J. Am. Chem. Soc.122:9692–9702. Similar approaches can be applied to growth of othercore-shell nanostructures. See, for example, U.S. Pat. No. 6,207,229(Mar. 27, 2001) and U.S. Pat. No. 6,322,901 (Nov. 27, 2001) to Bawendiet al. entitled “Highly luminescent color-selective materials.”

Growth of homogeneous populations of nanofibers, including nanofiberheterostructures in which different materials are distributed atdifferent locations along the long axis of the nanofibers is describedin, e.g., published PCT application numbers WO 02/17362, and WO02/080280; Gudiksen et al. (2002) “Growth of nanowire superlatticestructures for nanoscale photonics and electronics” Nature 415:617–620;Bjork et al. (2002) “One-dimensional steeplechase for electronsrealized” Nano Letters 2:86–90; Wu et al. (2002) “Block-by-block growthof single-crystalline Si/SiGe superlattice nanowires” Nano Letters 2,83–86; and U.S. patent application 60/370,095 (Apr. 2, 2002) toEmpedocles entitled “Nanowire heterostructures for encodinginformation.” Similar approaches can be applied to growth of otherheterostructures and applied to the various devices, methods and systemsherein.

In some embodiments the nanofibers used to create enhanced surface areascan be comprised of nitride (e.g., AlN, GaN, SiN, BN) or carbide (e.g.,SiC, TiC, Tungsten carbide, boron carbide) in order to create nanofiberswith high strength and durability. Alternatively, such nitrides/carbidesare used as hard coatings on lower strength (e.g., silicon or ZnO)nanofibers. While the dimensions of silicon nanofibers are excellent formany applications requiring enhanced surface area (e.g., see, throughoutand “Structures, Systems and Methods for Joining Articles and Materialsand Uses Therefore,” filed Apr. 17, 2003, U.S. Ser. No. 60/463,766,etc.) other capacitor applications can require nanofibers that are lessbrittle and which break less easily. Therefore, some embodiments hereintake advantage of materials such as nitrides and carbides which havehigher bond strengths than, e.g., Si, SiO₂ or ZnO. The nitrides andcarbides are optionally used as coatings to strengthen the weakernanofibers or even as nanofibers themselves.

Carbides and nitrides can be applied as coatings to low strength fibersby deposition techniques such as sputtering and plasma processes. Insome embodiments, to achieve high strength nanocoatings of carbide andnitride coatings, a random grain orientation and/or amorphous phase isgrown to avoid crack propagation. Optimum conformal coating of thenanofibers can optionally be achieved if the fibers are growingperpendicular to a substrate surface. The hard coating for fibers insuch orientation also acts to enhance the adhesion of the fibers to thesubstrate. For fibers that are randomly oriented, the coating ispreferential to the upper layer of fibers. Further information oncoating nanostructure surfaces (e.g., to deposit a dielectric layer orto construct a second electrode plate) is presented herein.

Low temperature processes for creation of silicon nanofibers areachieved by the decomposition of silane at about 400° C. in the presenceof a gold catalyst. However, as previously stated, silicon nanofiberscan be too brittle for some applications to form a durable nanofibermatrix (i.e., an enhanced surface area). Thus, formation and use of,e.g., SiN is optionally utilized in some embodiments herein. In thoseembodiments, NH₃, which has decomposition at about 300° C., is used tocombine with silane to form SiN nanofibers (also by using a goldcatalyst). Other catalytic surfaces to form such nanofibers can include,e.g., Ti, Fe, etc.

Forming carbide and nitride nanofibers directly from a melt cansometimes be challenging since the temperature of the liquid phase istypically greater than 1000° C. However, a nanofiber can be grown bycombining the metal component with the vapor phase. For example, GaN andSiC nanofibers have been grown (see, e.g., Peidong, Lieber, supra) byexposing Ga melt to NH₃ (for GaN) and graphite with silane (SiC).Similar concepts are optionally used to form other types of carbide andnitride nanofibers by combing metal-organic vapor species, e.g.,tungsten carbolic [W(CO)6] on a carbon surface to form tungsten carbide(WC), or titanium dimethoxy dineodecanoate on a carbon surface to formTiC. It will be appreciated that in such embodiments, the temperature,pressure, power of the sputtering and the CVD process are all optionallyvaried depending upon, e.g., the specific parameters desired in the endnanofibers. Additionally, several types of metal organic precursors andcatalytic surfaces used to form the nanofibers, as well as, the corematerials for the nanofibers (e.g., Si, ZnO, etc.) and the substratescontaining the nanofibers, are all also variable from one embodiment toanother depending upon, e.g., the specific enhanced nanofiber surfacearea capacitor to be constructed.

The present invention can be used with structures that may fall outsideof the size range of typical nanostructures. For example, Haraguchi etal. (U.S. Pat. No. 5,332,910) describes nanowhiskers which areoptionally used herein in design and construction of capacitors.Semi-conductor whiskers are also described by Haraguchi et al. (1994)“Polarization Dependence of Light Emitted from GaAs p-n junctions inquantum wire crystals” J. Appl. Phys. 75(8):4220–4225; Hiruma et al.(1993) “GaAs Free Standing Quantum Sized Wires,” J. Appl. Phys.74(5):3162–3171; Haraguchi et al. (1996) “Self Organized Fabrication ofPlanar GaAs Nanowhisker Arrays”; and Yazawa (1993) “SemiconductorNanowhiskers” Adv. Mater. 5(78):577–579. Such nanowhiskers areoptionally nanofibers of the invention. While the above references (andother references herein) are optionally used for construction anddetermination of parameters of nanofibers of the invention, those ofskill in the art will be familiar with other methods of nanofiberconstruction/design, etc. which can also be amenable to the methods anddevices herein.

Some embodiments herein comprise methods for improving the density andcontrol of nanowire growth as is relates to generating a nanostructuredsurface coating of substrates. Such methods include repetitive cyclingof nanofiber synthesis and gold fill deposition to make “nano-trees” aswell as the co-evaporation of material that will not form a siliconeutectic, thus, disrupting nucleation and causing smaller wireformation.

Such methods are utilized in the creation of ultra-high capacity surfacebased structures through nanofiber growth technology for, e.g.,nanofiber based capacitors. Use of single-step metal film type processin creation of nanofibers limits the ability to control the startingmetal film thickness, surface roughness, etc., and, thus, the ability ofcontrol nucleation from the surface.

In some embodiments of nanofiber enhanced surfaces it can be desirableto produce multibranched nanofibers. Such multibranched nanofibers couldallow an even greater increase in surface area than would occur withnon-branched nanofiber surfaces. To produce multibranched nanofibersgold film is optionally deposited onto a nanofiber surface (i.e., onethat has already grown nanofibers). When placed in a furnace, fibersperpendicular to the original growth direction can result, thus,generating branches on the original nanofibers. Colloidal metalparticles can optionally be used instead of gold film to give greatercontrol of the nucleation and branch formation. The cycle of branchingoptionally could be repeated multiple times to generate additionalbranches. Eventually, the branches between adjacent nanofibers couldoptionally touch and generate an interconnected network. Sintering isoptionally used to improve the binding of the fine branches.

In yet other capacitor embodiments, it is desirable to form finernanofibers (e.g., nanowires). To accomplish this, some embodimentsherein optionally use a non-alloy forming material during gold or otheralloy forming metal evaporation. Such material, when introduced in asmall percentage can optionally disrupt the metal film to allow it toform smaller droplets during wire growth and, thus, correspondinglyfiner fibers.

In yet other embodiments, post processing steps such as vapor depositionof materials can allow for greater anchoring or mechanical adhesion andinterconnection between nanofibers, thus, improving mechanicalrobustness in applications requiring additional strength as well asincreasing the overall surface to volume of the nanostructure surface.Additionally, typical embodiments herein have deposition of material(s)to form the dielectric.

It should be appreciated that specific embodiments and illustrationsherein of uses or devices, etc., which comprise nanofiber enhancedsurface area capacitors should not be construed as necessarily limiting.In other words, the current invention is illustrated by the descriptionsherein, but is not constrained by individual specifics of thedescriptions unless specifically stated. The embodiments areillustrative of various uses/applications of the enhanced surface areananofiber surface capacitors and constructs thereof. Again, theenumeration of specific embodiments herein is not to be taken asnecessarily limiting on other uses/applications which comprise theenhanced surface area nanofiber structures of the current invention.

In some embodiments, the invention comprises methods to selectivelymodify or create enhanced surface area substrates as well as suchenhanced substrates themselves and capacitor devices comprising thesame. As will be appreciated, and as is described herein, such methodsand devices are applicable to a wide range of uses and can be created inany of a number of ways (several of which are illustrated herein).

As will be appreciated, the enhanced surface areas provided by surfacescontaining nanofibers can provide significant advantages as an integralpart of a capacitor. However, in some embodiments, e.g., inmanufacturing or as required by some devices, multiple capacitors ormultiple nanofiber areas to be incorporated into capacitors are createdon the same substrate. Therefore, some embodiments herein comprisemethods that can allow spatially controlled chemistry to be applied tonanofiber-enhanced surfaces (e.g., application of dielectric material(s)and/or material(s) to comprise an opposing electrode plate, etc.),and/or to spatially control the placement of the nanofibers themselvesupon the substrate. Such control can facilitate the utility of enhancednanofiber surfaces in real applications.

Several approaches are included in the embodiments herein forselectively patterning areas of nanofiber growth or placement onsubstrates so as to generate spatially defined regions to which to applyspecific chemistry (e.g., dielectric deposition). In such approaches,the term “substrate” relates to the material upon which the wires aregrown (or, in some embodiments, placed or deposited). In differentsituations, substrates are optionally comprised of, e.g., silicon wafer,glass, quartz, or any other material appropriate for VLS based nanowiregrowth or the like. However, in typical embodiments wherein thenanofibers are to be used in situ, the substrate is preferablyelectrically conductive.

In some embodiments herein, micro-patterning of enhanced surface areasubstrates is optionally created by lithographically applying planarregions of gold to a substrate as the standard growth initiator throughuse of conventional lithographic approaches which are well known tothose of skill in the art. Nanofibers (e.g., VLS nanowires) are thengrown, e.g., in the manner of Peidong Yang, Advanced Materials, Vol. 13,No. 2, January 2001.

In other embodiments, patterning can be created by chemically precoatinga substrate through conventional lithographic approaches so thatdeposition of gold colloids is controlled prior to growth of nanofibers(e.g., by selective patterning of thiol groups on the substratesurface). In yet other embodiments, nanofibers are optionally pre-grownin a conventional manner well known to those of skill in the art (see,e.g., above) and then selectively attached to regions of the substratewhere the spatially defined pattern is required. Of course, in yet otherembodiments, “lawns” of nanofibers forming an enhanced surface areasubstrate are selectively patterned through removal of nanofibers inpreselected areas. Other embodiments can optionally comprise nanofiberlawns that have areas selectively cleared of nanofibers (thus, creatingnanofiber islands, etc.) or can have nanofibers only grown or depositedin certain selected areas (or any combinations thereof). Those of skillin the art will be aware of numerous other patterns, etc. which canoptionally be within embodiments herein.

While, certain methods of patterning,substrate/nanofiber/dielectric/etc. composition and the like areillustrated herein, it will again be appreciated that such areillustrative of the range included in the invention. Thus, suchparameters can be changed and still come within the range of theinvention. For example, as illustrated above, creation of enhancedsurface areas is optionally accomplished in any of a number of ways, allof which are encompassed herein. For example, as described in greaterdetail in co-pending and commonly assigned U.S. Patent Application Ser.No. 60/611,116 entitled “Nanostructured Thin Films and Their Uses,”filed Sep. 17, 2004, the entire contents of which are incorporated byreference herein, nanostructured surfaces can be made from a variety ofmaterials including insulating inorganic materials such as a nativeoxide layer or a deposited oxide or nitride layer. The insulatinginorganic material may also be formed form a deposited metal layer. Forexample, the insulating inorganic material may be selected from thegroup of materials including aluminum (Al), alumina (Al₂O₃), ZnO, SiO₂,ZrO₂, HfO₂, a hydrous form of these oxides, a compound oxide such asSiTiO₃, BaTiO₃ PbZrO₄ or a silicate. In one example, the film layer ismade from alumina or aluminum which can be deposited on the substrate(e.g., one or more electrode plates) using a variety of well-knowntechniques such as thermal evaporation and sputtering including physicalvapor deposition (PVD), sputter deposition, chemical vapor deposition(CVD), metallorganic CVD, plasma-enhanced CVD, laser ablation, orsolution deposition methods such as spray coating, dip coating, or spincoating etc. Ultra-thin metal films (e.g., films less than about 5 nm inthickness) may be deposited by atomic layer deposition (ALD) techniques.The thin film preferably has a thickness less than about 1000 nm, forexample, between about 5 and 400 nm, for example, between about 5 and200 nm, for example, between about 10 and 100 nm. The film layer maythen be configured to have a nanostructured surface, for example, byboiling the film layer, autoclaving it, etc. for a sufficient time(e.g., between about 3 to 60 minutes, for example, between about 5 to 30minutes) to convert the film into a highly ordered nanostructuredsurface having pore sizes less than about 200 nm. The nanostructuredfilm layer can also be formed by other means such as the formation ofporous alumina films via the anodization of aluminum metal in acidicsolution (e.g., phosphoric, oxalic, or sulfuric acid solutions). See,e.g., Evelina Palibroda, A. Lupsan, Stela Pruneanu, M. Savos, Thin SolidFilms, 256, 101 (1995), the entire contents of which are incorporated byreference herein. Other textured surfaces other than alumina or aluminumcan also be used including, for example, zinc oxide (ZnO) nanostructuredsurfaces and the other material surfaces described above.Low-temperature solution-based approaches to forming ZnO nanotexturedsurfaces are described, for example, in “Low Temperature Wafer-ScaleProduction of ZnO Nanowire Arrays,” Lori E. Greene et al., Angew. Chem.Int. Ed. 2003, 42, 3031–3034, the entire contents of which areincorporated by reference herein.

The nanostructured film layer can also optionally be coated orfunctionalized, e.g., to enhance or add specific properties. Forexample, polymers, ceramics, or small molecules can optionally be usedas coating materials. The optional coatings can impart characteristicssuch as water resistance, improved mechanical, optical (e.g.,enhancement of light coupling) or electrical properties. Thenanostructured film layer may also be derivatized with one or morefunctional moieties (e.g., a chemically reactive group) such as one ormore silane groups, e.g., one or more per-fluorinated silane groups, orother coatings such as diamond coatings, a hydrocarbon molecule, afluorocarbon molecule, or a short chain polymer of both types ofmolecules which may be attached to the film layer via silane chemistry.Those of skill in the art will be familiar with numerousfunctionalizations and functionalization techniques which are optionallyused herein (e.g., similar to those used in construction of separationcolumns, bio-assays, etc.).

For example, details regarding relevant moiety and other chemistries, aswell as methods for construction/use of such, can be found, e.g., inHermanson Bioconjugate Techniques Academic Press (1996), Kirk-OthmerConcise Encyclopedia of Chemical Technology (1999) Fourth Edition byGrayson et al. (ed.) John Wiley & Sons, Inc., New York and inKirk-Othmer Encyclopedia of Chemical Technology Fourth Edition (1998 and2000) by Grayson et al. (ed.) Wiley Interscience (print edition)/JohnWiley & Sons, Inc. (e-format). Further relevant information can be foundin CRC Handbook of Chemistry and Physics (2003) 83^(rd) edition by CRCPress. Details on conductive and other coatings, which can also beincorporated onto the nanostructured film layer of the invention byplasma methods and the like can be found in H. S. Nalwa (ed.), Handbookof Organic Conductive Molecules and Polymers, John Wiley & Sons 1997.See also, “ORGANIC SPECIES THAT FACILITATE CHARGE TRANSFER TO/FROMNANOCRYSTALS,” U.S. Ser. No. 60/452,232 filed Mar. 4, 2003 by Whitefordet al. Details regarding organic chemistry, relevant for, e.g., couplingof additional moieties to a functionalized surface can be found, e.g.,in Greene (1981) Protective Groups in Organic Synthesis, John Wiley andSons, New York, as well as in Schmidt (1996) Organic Chemistry Mosby, StLouis, Mo., and March's Advanced Organic Chemistry Reactions, Mechanismsand Structure, Fifth Edition (2000) Smith and March, Wiley InterscienceNew York ISBN 0-471-58589-0, and Ser. No. 10/833,944 filed Apr. 27,2004, entitled “Super-hydrophobic Surfaces, Methods of TheirConstruction and Uses Therefor.” Those of skill in the art will befamiliar with many other related references and techniques amenable forfunctionalization of surfaces herein.

While the foregoing invention has been described in some detail forpurposes of clarity and understanding, it will be clear to one skilledin the art from a reading of this disclosure that various changes inform and detail can be made without departing from the true scope of theinvention. For example, all the techniques and apparatus described abovecan be used in various combinations. All publications, patents, patentapplications, or other documents cited in this application areincorporated by reference in their entirety for all purposes to the sameextent as if each individual publication, patent, patent application, orother document were individually indicated to be incorporated byreference for all purposes.

1. An electric capacitor, comprising at least a first electrode surface,which electrode surface comprises a plurality of nanofibers, wherein adensity of the plurality of nanofibers ranges from about 0.11 nanofiberper square micron or less to at least about 1000 nanofibers per squaremicron, from about 1 nanofiber per square micron or less to at leastabout 500 nanofibers per square micron, from about 10 nanofibers persquare micron or less to at least about 250 nanofibers per squaremicron, or from about 50 nanofibers per square micron or less to atleast about 100 nanofibers per square micron.
 2. The capacitor of claim1, wherein the surface comprises a conductive material.
 3. The capacitorof claim 2, wherein the conductive material comprises a metal, asemiconducting material, a polymer, or a resin.
 4. The capacitor ofclaim 1, wherein one or more of the surface or the members of theplurality of nanofibers comprises silicon.
 5. The capacitor of claim 1,wherein the plurality of nanofibers comprises the same composition asthe composition of the first surface.
 6. The capacitor of claim 1,wherein the plurality of nanofibers comprises a different compositionfrom the composition of the first surface.
 7. The capacitor of claim 1,wherein the plurality of nanofibers is grown on the face of the surface.8. The capacitor of claim 1, wherein the plurality of nanofibers isdeposited on the face of the surface.
 9. The capacitor of claim 1,further comprising a dielectric which comprises a nonconductive materialand which covers substantially all members of the plurality ofnanofibers.
 10. The capacitor of claim 9, wherein the dielectriccomprises an oxide, a nitride, a polymer, a ceramic, a resin, aporcelain, a mica containing material, a glass, a vacuum, a rare earthoxide, a gas, or other typical dielectrics used in electroniccapacitors.
 11. The capacitor of claim 10, wherein the dielectriccomprises a grown oxide layer.
 12. The capacitor of claim 10, whereinthe dielectric comprises a naturally occurring oxide layer.
 13. Thecapacitor of claim 10, wherein the dielectric comprises silicon oxide.14. The capacitor of claim 10, wherein the oxide layer comprises athickness of from about 1 nm or less to about 1 um, from about 2 nm orless to about 750 nm, from about 5 nm or less to about 500 nm, fromabout 10 nm or less to about 250 nm, or from about 50 nm or less toabout 100 um.
 15. The capacitor of claim 10, wherein the oxide layer.comprises a thickness substantially equivalent to the thickness of theelectrode surface.
 16. The capacitor of claim 1, further comprising asecond electrode surface, which second surface comprises a layer ofmaterial deposed upon the dielectric covering the plurality ofnanofibers.
 17. The capacitor of claim 16, wherein the second surfacematerial comprises a conductive material.
 18. The capacitor of claim 17,wherein the second surface comprises a metal, a semiconducting material,a polymer, or a resin.
 19. The capacitor of claim 18, wherein the secondsurface comprises an evaporated or sputtered electrically conductingmaterial.
 20. The capacitor of claim 19, wherein the electricallyconducting material comprises aluminum, tantalum, platinum, nickel, asemiconducting material, polysilicon, titanium, titanium oxide, anelectrolyte, or gold.
 21. The capacitor of claim 1, wherein a length ofthe members of the plurality of nanofibers ranges from about 1 micron orless to at least about 500 microns, from about 5 micron or less to atleast about 150 microns, from about 10 micron or less to at least about125 microns, or from about 50 micron or less to at least about 100microns; and wherein the diameter of the members of the plurality ofnanofibers ranges from about 5 nm or less to at least about 1 micron,from about 10 nm or less to at least about 500 nm, from about 20 nm orless to at least about 250 nm, from about 20 nm or less to at leastabout 200 nm, from about 40 nm or less to at least about 200 nm, fromabout 50 nm or less to at least about 150 nm, or from about 75 nm orless to at least about 100 nm.
 22. A device comprising the capacitor ofclaim 1, 9, or
 16. 23. The device of claim 22, wherein the devicecomprises a timepiece, a watch, a radio, a remote control device, ananodevice, a medical prosthetic, or a medical implant device.
 24. Anelectric capacitor, comprising at least a first electrode surface, whichelectrode surface comprises a plurality of nanofibers, wherein a densityof the members of the plurality of nanofibers increases the surface areaof the first electrode surface at least 1.5 times to at least 100,000times or more, at least 5 times to at least 75,000 times or more, atleast 10 times to at least 50,000 times or more, at least 50 times to atleast 25,000 times or more, at least 100 times to at least 10,000 timesor more, or at least 500 times to at least 1,000 times or more greaterin comparison to an area of electrode surface without nanofibers, whicharea comprises a substantially equal footprint.
 25. An electriccapacitor, comprising at least a first electrode surface, whichelectrode surface comprises a plurality of nanofibers, wherein the faradcapacity of the capacitor comprises from about at least 1.5 times to atleast 100,000 times or more, at least 5 times to at least 75,000 timesor more, at least 10 times to at least 50,000 times or more, at least 50times to at least 25,000 times or more, at least 100 times to at least10,000 times or more, or at least 500 times to at least 1,000 times ormore greater in capacity in relation to a capacitor having an electrodesurface of substantially equal footprint but not comprising a pluralityof nanofibers.
 26. A capacitor comprising a supporting substrate havingat least a first electrode surface, a nanostructured thin film layercomprising alumina or aluminum deposited on at least a region of thesurface, and a hydrophobic coating deposited on the film layer.
 27. Thecapacitor of claim 26, wherein the hydrophobic coating comprises adiamond-like carbon coating.